The present invention relates to ink jet printing, and more particularly to an apparatus and method for detecting whether or not ink droplets are being properly jetted from the nozzles of a printing head.
Ink jet printing apparatus of the type to which the present invention relates are disclosed in Japanese Patent Publication Nos. 12138/1978, 39495/1976, and 45698/1978. These publications disclose ink jet printing apparatus wherein ink droplets are jetted from a plurality of nozzles in response to electrical signals applied to piezoelectric crystal elements to cause pulses in pressure chambers associated with the nozzles.
On demand ink jet printing apparatus of this type sometimes fails to properly jet ink droplets from the nozzles. The reason for this is that the nozzle orifices become blocked by air bubbles in the printing head, or become partially obstructed or clogged by dust, dirt or other foreign particles, or by dried ink, particularly if the printing head is not used for some time. When this occurs, printing quality suffers either because the ink droplets miss their target or because some are not jetted at all. In that event, it is necessary that the blocked or clogged orifices be cleaned so that proper performance is restored to the printing head.
In the past, it often has been necessary to visually inspect the nozzle orifices and to witness the printing produced thereby to determine whether the nozzle orifices are clear. Also, the corrective action necessary to clear the orifices and restore the printing head to proper operation has, in the past, required manual labor. This is troublesome and time consuming. Devices have been proposed to carry out this procedure without visual inspection and manual labor, but these devices, in many instances, fall short of producing satisfactory results.
It is, therefore, a main object of this invention to overcome the problems and shortcomings of the prior art and to provide a method and an apparatus for accurately determining when an ink jet device has failed, as described above.
It is also an important object of this invention to provide such a method and apparatus whereby the necessary corrective action can be performed easily and automatically to restore the device to proper operation.
The accompanying drawings which are incorporated in and constitute a part of this specification, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.